1. Technical Field
The technical field relates to a lens barrel with which the focal length can be changed.
2. Description of the Related Art
Conventional digital cameras make use of a zoom lens system with which the focal length can be varied while the object distance of a subject that is in focus (hereinafter also referred to as the subject distance) is kept substantially constant. For example, zoom lens systems are employed in compact digital cameras and digital cameras with interchangeable lenses.
With a conventional lens barrel, for example, as the zoom mechanism operates, the focus lens unit including the focus lens is moved in the optical axis direction by a cam mechanism. This allows the focal length to be varied while the subject distance is kept substantially constant (see, for example, Japanese Laid-Open Patent Application 2006-113289).
A phase difference detection system has been employed as the auto-focus system with conventional interchangeable lens digital cameras.
More recently, however, an interchangeable lens digital camera has been proposed that makes use of a contrast detection system for auto-focusing. With this contrast detection system, for example, the focus lens unit is moved in the optical axis direction while evaluation values at various positions of the focus lens unit are found on the basis of image data. The focus lens unit is moved until the evaluation value goes past its peak, after which the evaluation value is returned to its maximum position to focus the subject image (an optical image of the subject). Thus, in auto-focusing by contrast detection, it is necessary to move the focus lens unit back and forth in the optical axis direction.
Also, since the focus needs to be continued during the capture of moving pictures, the focus lens unit has to be continuously moved back and forth and the peak of the evaluation value detected.
Thus, when a contrast detection system is used, since the focus lens unit is moved in the optical axis direction, making the focus lens unit smaller is preferable when drive speed is taken into account.